1. Field of the Invention
This invention relates to polyurethane materials, particulary plyurethane elastomers which are resistant to sagging prior to cure when applied on non-horizontal surfaces.
2. Description of the Prior Art
Conventional polyurethane-base elastomers employed as adhesives, sealants, caulks or surface coatings suffer a serious disadvantage in that they tend to sag and run off or drip down when applied on non-horizontal surfaces. There have been many attempts to overcome this disadvantage. It has been known to add thickeners such as fillers, powders, and the like to one or both of the components of the polyurethane composition so that, when mixed, the composition will have sufficient viscosity to resist sagging. However, the use of such thickeners in amounts which are effective cause problems in the handling of the components. For example, the components become so viscous as to present difficulties in obtaining the proper mixing of the two components in conventional applicator devices. An alternate approach to improving sag resistance of polyurethane compositions is to increase the amount of catalyst in the urethane composition to promote quicker thickening. This approach is generally unsatisfactory in dealing with large batches because of the higher exotherm and the unduly shortened set time encountered.
The use of amines, such as those of U.S. Pat. No. 3,654,370, as the B-component is impractical. The reaction of the amine with the A-component is so fast that the mixed elastomer would become immediately set upon mixing of the A- and B-components. Also, cyanoalkylated derivatives of certain amines, such as those of U.S. Pat. No. 3,666,788 although suitable as the B-component in some coating compositions, are unsuitable when the mixed elastomer system must remain workable for several minutes.
The addition of amines to polyurethane compositions to increase the sag resistance is known. However, the general approach is to add an amine to the B-component and add an amount of isocyanate equivalent to the amine to thereby form a thickened B-component. The disadvantage of this method is that to obtain the desired sag resistance in the mixed elastomer, it may be necessary to thicken the B-component to an extent that it becomes unnecessarily difficult to work with.
Another approach to improving sag resistance involves the addition of certain di- or multi-primary amines to the B-component of polyurethane compositions as is disclosed in U.S. Pat. No. 3,714,127. However, upon the mixing of the two components of such polyurethane compositions, there is generally a lag in the thickening action and the mixed elastomer will tend to sag if applied immediately after mixing. If very large amounts of the amines are employed to reduce the time required to thicken the mixed elastomer, the exotherm of the mixed system is generally higher and the set time of a large batch would be significantly shortened. Regardless of the amount of such amines which are incorporated into the composition, there results a mixed polyurethane composition in which the workability or consistency is constantly changing.
From the above, it is apparent that, although there have been many attempts to improve the sag resistance of polyurethane compositions without adversely affecting other properties of the mixed elastomer, none has been entirely satisfactory.
It is an object of the present invention to provide a polyurethane elastomer composition which, when mixed, will not sag when applied in thick films or layers on non-horizontal surfaces. It is also an object of the present invention to provide a polyurethane elastomer composition which is easy to handle and does not involve extremely viscous components. Further, it is an object of the present invention to provide a modified polyurethane composition which, when mixed, thickens immediately to provide sag resistance, yet substantially retains the long set times and cured elastomer properties characteristic of unmodified systems.
The advantages and other objects of our invention will become apparent to those skilled in the art in view of the aforementioned background, the following discussion and accompanying examples.